Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic system.
Description of the Related Art
Conventionally, as an image forming apparatus such as a laser beam printer, an image forming apparatus is known which adopts an in-line color system and which is constituted by a plurality of image forming stations in which a photosensitive drum as an image bearing member is arranged in plurality in a rotation direction of an intermediate transfer member. In the image forming apparatus, an electrostatic latent image created on the photosensitive drum in each of the plurality of image forming stations is developed into a toner image by developing means, and the resultant is primarily transferred to the intermediate transfer member. By similarly repeating primary transfers in the plurality of image forming stations in this step, a full-color toner image is formed on the intermediate transfer member. Subsequently, the full-color toner image is secondarily transferred to recording material and, furthermore, the full-color toner image is fixed to the recording material by fixing means. An image formed by the series of image forming operations must represent output of an image and density intended by a user. In addition, a full-color image created by the plurality of image forming stations requires tinge reproducibility and stability.
In consideration thereof, Japanese Patent Application Laid-open No. H8-227222 proposes a method of increasing a tinge selection range by changing a developing bias or a rotational speed of a developing roller as a developer bearing member or the like according to purpose. In addition, Japanese Patent Application Laid-open No. 2013-210489 proposes a method for overcoming problems such as toner scattering and image thinning which accompany an increase in a tinge selection range or an improvement in density. This method enables an image with an increased tinge selection range or a high-density image to be output without causing image-related problems by reducing a peripheral velocity of a photosensitive drum to increase a peripheral velocity ratio between the photosensitive drum and a developing roller. Furthermore, in a case of high-density printing such as solid black, by forming a development contrast such that all of toner on a developing roller is developed onto a photosensitive drum, a tinge selection range is increased, high density is realized, and stabilization is provided while minimizing an effect of a potential fluctuation of the photosensitive drum and the like.